In the U.S. Pat. No. 6,219,948 B1 issued to Itzchak Bar-Yona et al has been disclosed a kind of displaying unit which includes a housing having at least one window-like opening; at least one lenticular panel mounted in the housing behind the window-like opening, the lenticular panel having front and rear faces, the local length of the length of the lenses being substantially equal to their width; at least one displaceable, lightweight, substantially planar indicia carrier in the form of a replaceable film or sheet disposed inside the housing; an edge of the indicia carrier at least indirectly freely abutting against a cam; a high efficiency, low-energy consumption, battery powered DC drive including a DC motor complied to the cam for periodically displacing the indicia carrier for a distance at least equaling the distance between two adjacent lenses of the panel; and a guide facilitating smooth reciprocating movement of the indicia carrier in juxtaposition with the rear face of the lenticular panel, whereby displaying the indicia carrier causes the constituent elements of one of the two or more images to be replaced by constituent elements of another one of the two or more images.
Although the above-mentioned unit can continuously display two or more images of the indicia carrier, the change of the images is achieved by the up and down movement of indicia carrier actuated by a motor or cam. This display unit, not only has the drawback of complicated structure, but also its transmission or drive requires balance weight to match the cam, and although the indicia carrier is made of a lightweight paper, it must be flat and straight, in addition a paper is liable to be affected with damp, which will cause the paper to be deformed, thereby the movement speed will be seriously affected. And the indicia carrier cannot be operated properly, resulting in the fact that the images cannot be precisely displayed and even leading to the superposition of the images. In order to overcome the problems occurring in the indicia carrier, a scheme has been proposed to stick or print images on a film or plastic plate. But this method is not only expensive in price, but also, in the processing, the images are easy to have torsions or to lose the finest details of images.